The present invention relates to a method for preparing an oxidizing material, to the oxidizing material thus prepared, and to a method for treating effluents, and in particular to method for treating photographic effluents.
Many manufacturing or processing methods produce effluents that cannot be released directly into the sewers because of their composition. One example is that of the photographic industry, in which exposed films and papers pass successively through several processing steps (or xe2x80x9cbathsxe2x80x9d) that produce effluents rich in chemicals. Such processing methods for photographic films are well known (see, for example, Chimie et Physique Photographiques, Pierre Glafkides, Vol. 2, Cap. XL, pages 947-967).
Conventionally, the processing of photographic products comprises a development step and a de-silvering step. The de-silvering step comprises the bleaching of the photographic product, which consists of converting metallic silver into silver ions, followed by fixing, which consists of eliminating the silver ions contained in the photographic product. Conventionally, the photographic processing steps can also include wash and stabilizing steps.
Photographic products are generally developed automatically and as quickly as possible. During processing, the product passes through each of the steps described above. When the photographic product passes through the successive steps, non-negligible quantities of chemicals are carried over from one tank to the next, either by the photographic product itself or by the drive belts that convey the photographic product. These chemicals build up in the processing baths and thereby reduce their efficacy. The faster the photographic products are processed, the worse is the contamination of baths by the carry-over of chemicals. To counter this contamination, wash baths are intercalated between successive processing baths. In particular, after passage through a fixing or bleaching-fixing bath, the film passes through several wash baths before it enters the stabilizing bath.
The wash baths that come after the fixing step contain many substances such as sulfites, thiosulfates and (or) ammonium salts used in the fixing baths, the sulfites and thiosulfates possibly deriving also from the developer. These wash baths cannot be discarded directly into the sewers and must be treated first to eliminate inorganic salts such as sulfites, thiosulfates, ammonium, and other organic by-products that raise the COD of the baths and are particularly harmful to the environment.
In addition, because the development process takes place in an aqueous phase, the growth of micro-organisms, in particular in pre-baths, stabilizing baths and wash baths commonly occurs, worsening when the quantities of water consumed are reduced. The growth of micro-organisms such as molds and yeasts, if not controlled, causes the formation of sludge that clog the plant, degrade the processing bath, and so impair the quality of photographic image. Also, the presence of micro-organisms, especially bacteria, causes a biofilm to form on the walls of the processing tanks and on the film drive rollers and wheels, so that the machinery has to be shut down for cleaning.
The use of control agents to prevent or limit bacterial growth in processing baths is common practice. Unfortunately, certain bacterial growth control agents are very sensitive to the presence of sulfites and thiosulfates found in washing water and are broken down before they can fully act. To compensate for this breakdown, excess quantities are used relative to the exact amount required. In this case the water discharged into the environment contains large quantities of bacterial growth control agents, which causes problems in wastewater treatment plants that exploit the action of micro-organisms for effluent treatment.
L. M. Liz-Marzan and A. P. Philipse, in J. Phys. Chem., American Chemical Society, 1995, 99, 15120-15128, describe the synthesis of metal particles in aqueous dispersions of imogolite by reduction of their salts with sodium borohydride. Very stable dispersions of metallic nanoparticles are obtained and can be used for the preparation of catalysts.
The present invention provides a method for preparing a material that minimizes the occurrence and growth of micro-organisms in processing water in order thereby to reduce the quantities of control agents that have to be used.
The present invention provides also a material that rids processing water of pollutant by-products so as to obtain effluents that comply with regulatory requirements.
The present invention provides also a material to rid processing water of pollutant by-products that generate unwanted reactions with bacterial growth control agents, in order thereby to extend the life of said agents.
The present invention relates to a method for preparing an oxidizing material comprising the step of (i) dispersing in colloidal form a metal or a metal compound in an aqueous solution of an inorganic aluminosilicate polymer, said aluminosilicate being able to form an inorganic gel, and said metal or metal compound being able to cause the oxidation of oxidizable compounds and (or) micro-organisms to be eliminated, and the step of (ii) adding a base to cause said aluminosilicate to gel.
The present invention also concerns a material obtainable by the method described above, as well as its use to oxidize, in the presence of water, oxidizable compounds and (or) micro-organisms to be eliminated.
The invention also concerns a method for treating an aqueous solution liable to contain oxidizable compounds to be eliminated and (or) to harbor micro-organisms, as well as a device for carrying out said method. The method comprises contacting the aqueous solution with said oxidizing material. It is especially efficient for the treatment of photographic baths, in particular wash baths after the fixing step, because it rids such baths of micro-organisms and oxidizable chemical by-products. The xe2x80x9cmicro-organisms to be eliminatedxe2x80x9d can be in particular algae, fungi, bacteria and yeasts. The xe2x80x9coxidizable chemicals to be eliminatedxe2x80x9d can be in particular inorganic or organic by-products considered as pollutants either with regard to aqueous the solution to be treated or in a general way with regard to the environment, for example sulfite and ammonium ions, surfactants, etc.